Filament orientation process



Jam 1968 s. K GARIBIAN ETAL 3,364,294

FILAMENT ORIENTATION PROCESS Filed Sept. 20, 1965 I 2 Sheets-Sheet 1INVENTORS SARK/S K. GARIBIAN AMPB LL 1 s. K. GARIBIAN ETAL 3,

FILAMENT ORIENTATION PROCESS Filed Sept. 20, 1965 2 Sheets-Sheet 2 Q Q M'FIG.3.

INVENTORS SARKIS K. GA'RIBIAN WILLIAM L. CAMP ELL United States Patent3,364,294 FILAMENT ORIENTATION PROCESS Sarkis K. Garibian and William L.Campbell, Cary, and

William R. Hocutt, Raleigh, NC, assignors to Monsanto Company, St.Louis, Mo., a corporation of Delaware Filed Sept. 20, 1965, Ser. No.488,628 5 Claims. (Cl. 264--290) ABSTRACT OF THE DISCLOSURE A heavydenier tow drawing process wherein a polyester tow is uniformly drawn byapplication of dielectric energy. The operation is found particularlyefficient in the case of polyester drawing due to the coincidence of thepreferred drawing temperature and maximization of the dielectric lossfactor at a temperature range of from about 90 to 100 C.

This invention relates to a process for effecting the orientation ofsynthetic filaments in a highly uniform manner. More particularly, theinvention is concerned with the problem of orienting polyethyleneterephthalate filaments when processed in the form of heavy denier towscomposed of densely spaced filaments.

There is disclosed in US. Patent 2,465,319 to Whinfield and Dickson theproduction of highly useful fibers composed of polyethyleneterephthalate, which includes the steps of preparing the polymer,melt-spinning the polymer to form substantially unoriented filaments anddrawing the filaments to a permanent increase in length to yieldtenacious, oriented fibers. As is well known, the drawing of filamentsformed from synthetic organic polymers gives rise to macromolecularorientation along the filamentary axis, as evidenced by characteristicX-ray patterns, along with increased tenacity and reduced elongation atbreak.

In the textile industry, the various conventional drawing processes,involving the passing of a yarn or tow over, between, or in contact withheated surfaces such as pins, plates and heated gas zones, have provedgenerally satisfactory for drawing textile and even industrial deniercontinuous filament yarns. However, these various proc esses have notbeen found entirely satisfactory for draworienting the much heavierdenier tows typically encountered, for example, in staple fiberproduction. In staple production, it has been found highly desirable,out of considerations for production economy, to combine several hoursof production from a number of spinning machines into tows ranging indenier to as high as 2.5 and drawing the constituent filamentssimultaneously.

In attempting to adapt previously known drawing processes to the drawingof such heavy denier tows of polyethylene terephthalate, it has beenfound that the tow does not draw in a uniform manner; that is to say,random lengths of the various filaments pass through the drawing stepwith little or no orientation. This is because a uniform and sufficientheating of the individual filaments comprising a tow of this size cannotbe achieved by normal tow heating techniques which employ variousarrangements and configurations of heated surfaces and zones and which,therefore, rely to a major extent upon heat transfer from filament tofilament; consequently, non-uniform drawing unavoidably results due totemperature variations across the filament bundle. In addition toofttimes serious variations in important physical properties, staplefiber cut from such non-uniformly oriented tows is particularlydeficient where such fibers are intended for use in the fabrication ofdyed fabrics in that partially oriented or substantially unorientedfibers or fiber sections dye to much deeper colors than the more fullyoriented members and appear in the fabric as flecks of darker color.

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Fabrics formed from staple fiber not possessing a high order ofuniformity in orientation will exhibit such an incidence of dyeingdefects as to be unacceptablefor many otherwise available markets.

In order to obtain the requisite uniformity in drawing heavy deniertows, it has therefore been found necessary, in most instances, to drawthe tow in the form of relatively thin, wide, sheet-like bundles in anattempt to minimize an otherwise undue inter-filament variation inexposure to the influence of conventional heating agents and to promoteuniform contact of the individual filaments with the heat source. In anattempt to realize the production economies available in the processingof heavy denier tows, a number of wet-drawing procedures have beenproposed involving the use of steam and aqueous or other inert fluidbath, which procedures have been commercially employed with varyingdegrees of success in obtaining uniformly drawn tows. However, even themore desirable of these wet-draw procedures have certain recognizeddisadvantages, among which are the necessity of a considerable amount ofexpensive auxiliary equipment (i.e. tanks, pumps, heaters, filters,etc.) large, costly ovens necessary to dry the wet-processed tow, and agenerally large machine space requirement to accommodate the severalbaths and sets of rolls which may be required. Furthermore, even themost successful wet-drawing procedures must be conducted with due regardfor tow bundle configuration; that is, very heavy denier tows (in theorder of 1 10 denier and greater) must be processed in the form ofrelatively wide ribbons in order that the tow density (measured indenier per inch of bundle width) does not exceed that level beyond whichnon-uniform heating of the individual filaments, resulting innon-uniform orientation, will unavoidably occur. For example, where itis desired to process a tow size on the order of 2x10 denier, it isfound that non-uniform drawing reaches undue levels where tow densityexceeds 100,000 denier per inch and the tow bundle must be maintained inthe form of ribbon at least 20 inches wide. Obviously, substantialeconomies, in terms of equipment, space and production, would berealized if either a narrower bundle or a heavier tow denier could beaccommodated.

On the other hand, the relativelyiless expensive and less involvedimplementation of previously disclosed dry drawing processes aredecidedly lacking in their ability to provide uniformly oriented highdenier tows. At best, even moderately heavy denier tows processedaccording to known dry-drawing methods must be handled in the form ofunduly wide ribbon shapes in order that the density of the filamentbundle does not exceed that level productive of non-uniform heating andconsequent erratic drawing. Though the tow density amenable toconventional drydrawing processes is not subject to precise definition,it has been found that filamentary bundles having a density of ten tofifteen thousand undrawn denier per inch may be drawn satisfactorily,while filament bundles having a density in excess of about 35,000undrawn denier per inch do not draw in a uniform manner when processedby the same methods. On the other hand, though satisfactory results maysometimes be obtained by utilizing the more proficient of thewet-drawing methods, as previously related, these operations arecharacterized by heavy equipment expense and process complications,while still entailing limitations as to bundle denier per unit width andbundle cross-sectional configuration.

With the foregoing problems and considerations in mind, it thereforebecomes an object of this invention to provide an improved process fordrawing heavy denier, substantially unoriented, polyethyleneterephthalate tows without resorting to the complications attendingconventional wetdrawing processes and without sacrifice to productquality.

A further object is to provide such a process in which the drawn towexhibits a high order of inter-filament uniformity in orientation and aconsequent low incidence of variation in fiber properties, particularlyas regards variations in dye receptivity. Other objects will becomeapparent from the following description, appended drawing and theclaims.

According to the present invention, the foregoing and other objects areattained in the practice of a process wherein a heavy denier, highdensity tow of substantially unoriented polyethylene terephthalatefilaments is draw-oriented under the influence of a dielectric field.More precisely, the most beneficial results are obtained by passing suchfilaments in the form of a tow having a density in excess of aboutthirty-five thousand undrawn denier per inch, measured across the widthof the tow bundle, through a preheating and moisturizing treatment,wherein the tow is heated to a temperature within the range of 50 to 100C. and a moisture level of at least 3 percent, preferably greater than 6percent is imparted thereto; thence passing the thus moistened andpreheated tow through a dielectric field while subjecting same to thedesired draw ratio, the dielectric field being characterized by afrequency of from 1 to 1200 megacycles per second, and a voltage of fromabout 2,000 to 25,000 volts. The tow is processed in a manner to insuremaximum uniformity of tension upon each of the individual filaments. Forgreater efliciency and uniformity in heat-up rate, the dielectric fieldis established in such a manner as to provide an increasing fieldintensity as yarn moisture decreases during heating. That is, as theyarn is heated in passing through the dielectric field, it willexperience a continuous decrease in moisture, with a consequent decreasein its dielectric loss properties, requiring, if a substantiallyconstant rate of heat evolution is to be maintained, an increasing fieldintensity. Also, it has been found that, if undesired arcing across theelectrodes defining the dielectric field is to be avoided whenprocessing yarn containing substantial levels of moisture, theelectrodes should be heated sufiiciently to avoid condensation of thevapor emanating from the heated yarn at least in those upstream regionsof higher yarn moisture level. This may be accomplished in any one ofseveral ways, such as sweeping the space surrounding the dielectricfield with heated, dry air or other gas and/ or providing auxiliaryradiant heaters in the chamber enclosing the dielectric electrode array.

As is well known, dielectric heating, also referred to aselectromagnetic heating, involves the application of high frequency,high voltage electrical energy to non-metallic materials. The frequencyrange normally employed in dielectric heating operations may vary from 1to 1200 megacycles per second; applied voltages at the electrodes arenormally in the range of 2,000 to 25,000 volts. These values areindicative of present-day practice and are not intended to imply thathigher frequencies and voltages cannot as well be employed.

High frequency heating is possible only in those materials that are atleast moderately molecularly polar. Polar molecules possess a pair ofelectrical charges of opposite polarity called dipoles. A dipolemolecule placed in a constant electrostatic field will attempt to alignitself with the potential gradient of the field. This motion isaccomplished by the interaction of the electrical field and the chargecenters of the molecule, thus creating an aligning torque called adipole moment. Molecules lacking such polarity are unaffected by a highfrequency electrostatic field. Also, certain molecules, even though theypossess dipoles, are little affected by electrical fields in that thedipole moments are substantially equal and opposing. Dielectric heatingis accomplished by utilization.

of ultra-high frequencies which elevate the molecules to a highlyagitated state, resulting in internally generated heat by molecularfriction. The more viscous materials offer greater resistance to suchmolecular agitation and,

consequently, require greater energy input to elevate the temperature toa given level.

The material to be heated is located between two sets of electrodes, oneof which is maintained at a high potential relative to the other. Thehigh potential force thus established forces the high frequency fieldthrough the material. This field, in passing through the material,creates a high degree of molecular motion throughout the cross section,resulting in a uniform temperature rise in the material regardless ofits thermal conductivity, provided the mass has equal density andmoisture content. The fact that most non-metallic materials are poorheat conductors leads to non-uniform heating when conventional modes ofheating are employed, such as convection, conduction, or radiantheating. When heating materials of thickness by such heat transfermechanisms, the outside surface necessarily becomes heated far morequickly than the interior regions. It thus becomes evident that a majoradvantage to be realized in dielectric heating is the uniformity intemperature to be achieved throughout the extremities of the mass and itis primarily by virtue of this attribute, when employed in the mannerhere disclosed, that one is enabled to conduct a substantiallydry-drawing process upon high density, heavy denier tows at levels oforientation uniformity heretofore not attained.

For a more detailed understanding of the practice of the presentinvention, reference shall now be had to the accompanying drawings asbeing illustrative of a typical implementation of the process and inwhich:

FIG. 1 is an overall view of one possible arrangement for conductingdrawing operations upon heavy denier tows according to the presentinvention wherein a suitable tow bundle is formed, passed through apreconditioning chamber to impart desired measures of temperature andmoisture content, the tow then being passed through feed and draw rollassemblies which are interposed by a dielectric heating oven, the towthen being gathered in bobbin form or the like by a suitable take-uparrangement;

FIG. 2 depicts, in plan view, an electrode assembly configurationproductive of dielectric field characteristics most amenable to thepractice of the present invention, and

FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. 2 showing thehorizontal and vertical spacing of the individual finger-type electrodesof the upper, high potential and lower, low potential electrodeassemblies.

In polyester spinning, as presently commercialized, it is impossible tospin from one spinning machine tows of sufiicient denier to enableeflicient staple fiber drawing. Consequently, it is necessary to plytogether numerous ends from creeled cans or bobbins to obtain thedesired total denier of at least 35,000, a figure dictated out ofconsiderations of economic feasibility and not necessarily operability.Thus, individual continuous filament bundles are gathered from aplurality of sources and directed through a suitable constant tensionmeans, not shown, in order to tension each of the individual filamentsto as uniform a degree as is practicable with present day devices. Anundue variation in individual filament tension will, as is well known,be reflected by an unacceptable degree of variation in individualfilament orientation, no matter the advantages of a particular drawingoperation.

After passing through the tension regulating means, the individualfilament bundles are caused to converge into a relatively flat, heavydenier tow 10 by means of a bar guide 12 or the like. The thusly formedtow may then be passed through a preconditioning chamber 14 wherein thedesired conditions of tow temperature and moisture content areestablished and maintained uniform along the length of tow beingprocessed.

It is to be understood that, though the following discussion willlargely be concerned with water as the moisturiz'ing agent, many otherpolar liquid mediums, such as the glycols, low molecular weightalcohols, and polar finishes, could as well be employed, though waterwould normally be employed out of economic considerations. The additionof a polar moisturizing agent functions to raise an otherwise lowdielectric loss factor that is characteristic of polyester tows. Theloss factor is a measure of the ability of a given material under givenconditions to absorb dielectric energy, which is thereby converted tointernally generated heat energy resulting in a rise in temperature.Although the instant drawing process may be conducted without raisingthe dielectric loss factor by polar moisture conditioning, thelimitations thus imposed on draw speed and draw ratio Will normally befound overly restrictive where production costs constitute a significantfactor. Likewise, the process may be practiced in the absence ofadvantages to be gained by preheating the tow, but with similarconsequences.

As symbolically indicated in FIG. 1, pre-heating and moisturizing may beaccomplished in a single operation by supplying, through inlet 16, aheated polar liquid under pressure which may be atomized or vaporizedwithin preconditioning chamber 14 to be uniformly deposited upon theindividual filaments of a suitably flared tow bundle. A trap line 1-8communicates with the lower regions of chamber 14 to carry off andrecirculate any moisturizing agent which is allowed to condense.

The residence time of the tow within chamber 14 and the quantity andtemperature of the moisturizing agent supplied thereto are regulated toimpart to the tow, as it departs the chamber through exit port 20, atemperature of at least 50 C. and a moisture content, in the case ofwater, of at least 3 percent, preferably 6-12 percent, if optimumprocessing speeds and efficiency of operation are to be realized. Themoisture content may, however, be varied up to as high as 30 percent byweight of tow where it is desired that the tow depart the drawingoperation with a relatively high residual moisture content, as may bedictated by certain after-treatments, such as washing, crimping andfinishing. It has been found that any attempt to operate with moisturecontents above 30 percent results in an undue proportion of thedielectric energy being absorbed merely to vaporize such excess moisturelevels, as well as to precipitate arcing between the electrodes,resulting in serious tow defects. Moisture conditioning has as itsprimary purpose the raising of the dielectric constant of the tow tothereby provide rapid heat-up to drawing temperature. In the case oftows of polyethylene tercphthalate, it has been found that a moisturecontent of from about 6 to 12 percent by weight of tow gives optimumresults, moisture levels above this range absorbing a disproportionateamount of dielectric energy requiring either or both relatively longelectrode assemblies and high field voltage where it is desired toextract the tow from the drawing operation in a relatively drycondition, i.e., below 0.5 percent moisture; on the other hand, anin-coming moisture content below 6 percent results in decreasing heat-uprates to the point that, at levels below 3 percent, the draw speed anddraw ratios which must be maintained for uniform draw-orientation aretoo low to obtain the throughput rates and levels of orientationnormally desired. An attempt to increase the throughput to conventionalspeeds when operating at such low moisture levels results in sporadicmigration of the draw point towards the draw roll; whereas, an increaseto draw ratios required to impart even conventional levels oforientation will result in migration of the draw point towards the feedroll, the migration in either direction being characterized by asporadic oscillation resulting in radom orientation values along thelength of the tow. We have discovered, therefore, that, if conventionaldraw speeds and ratios are to be accommodated, the tow must beintroduced to the dielectrically heated draw zone at a temperaturegreater than about 50 C. and 3 percent moisture, a level of at least 6percent being preferred. As before related, the moisture content shouldnot be allowed to exceed 12 percent where it is desired to extract thetow in a relatively dry condition, but the in-coming moisture contentmay vary up to 30 percent where it is desired to convey the tow tofurther processing operations in a moistened condition; at levels above30 percent however, energies absorbed through vaporization andconsequent arcing render such levels undesirable.

The tow, thusly preconditioned, is withdrawn from chamber 14 by feedroll assembly 22, which may comprise a pair of skew-mounted godets whichare preferably maintained at or near the temperature of the tow. The towthus enters the dielectric heating oven, generally indicated by numeral24, at a temperature greater than about 5-0" C. and a moisture contentgreater than 3 percent by weight of tow. The tow passes through thedielectric oven to engage draw roll assembly 26, the peripheral speed ofwhich is maintained at a constant difference above that of the feed rollassembly 22 to thereby impose the desired degree of elongation andconsequent orientation to the tow as it is heated to draw temperaturewithin oven 24. On departing the draw roll assembly, the tow may bepassed through a suitable guide 28, thence to other processing orthrough traverse guide 30 and take-up roll 32.

Referring to the details of the dielectric oven 2-4, the electrode arrayis seen to be enclosed within a housing 34, the interior surface ofwhich is provided with suitable metallic sheathing 38 to shield vicinalequipment from electrical interference due to high radio frequenciesemployed.

A conduit 40 communicates with the upstream region of the oven interiorto supply a continuous flow of heated, relatively dry gas, as by meansof a heater fan 42, which flow is exhausted from the downstream regionof the oven interior through exhaust port 44. By this arrangement, thespace surrounding the electrode arrangement is constantly swept by adry, heated gas to retard condensation of the volatilizing polarmoisturizing agent as the tow is being heated. Thus, high moisture towmay be processed without generating such moisture levels adjacent theelectrodes as will result in condensation thereon and consequent arcingbetween the electrodes and burning or melting of the tow. Such asweeping operation also has the advantage of maintaining a uniformtemperature throughout the oven interior. If desired, the heatingfunction of the sweep gas may be supplemented by auxiliary radiantheaters, not shown, which may be placed along the oven interior. Asshown, the electrode assembly may be mounted within the oven by means ofsuitable insulated mounting studs 46 which serve to electrically isolatethe electrodes from the housing 34. Heavy capacity leads 48 connect theupper and lower electrodes assemblies with a conventional dielectricgenerator, not shown. In that the details of the dielectric generator donot comprise a part of the present invention and are well known, adetailed discussion would not here be appropriate. It will suffice tounderstand that many generators of conventional design may be employedin the practice of the present invention to good advantage insofar asthey may be capable of rendering a field frequency of from 1 to 300megacycles per second at from about 2,000 to 25,000 volts.

For a more detailed showing of the configuration of the electrodeassembly per se, reference is made to FIGS. 2 and 3, wherein theassembly is seen to comprise an upper, high potential electrode assembly50 and a lower, low potential electrode assembly 52 which togethercomprise the total electrode array, generally denoted by numeral 54. Theupper and lower electrode assemblies 50, 52, which are of identicalconstruction and electrode spacing, are seen to comprise a bus bar 56supported at either end within the oven by the previously referred toinsulated studs 46. Extending from each bus bar is a plurality ofelectrode fingers of equal length and decreasing spacing as viewed fromleft to right in FIGS. 2 and 3 (the tow also passing from left toright). The electrode length and consequent capacity may be variedaccording to the drawing speed and percent moisture desired in thefinally drawn tow. The spacing between the upper, high potentialelectrode assembly 50 and the lower, grounded electrode assembly 52,which spacing is denoted by gap labeled G in FIG. 3, is dependent uponthe tow thickness being processed, it being desired that this verticalelectrode gap be of such dimension to pass the tow tangent to both theupper and lower fingers 58, 58, respectively. Where it is contemplatedthat tows of varying thickness will be processed, it will be founddesirable to mount either or both electrode assemblies so that thevertical gap G may be adjusted whereby any air gap between therespective fingers and the tow surface is maintained at a minimum. Undueair gaps between the tow surface and the electrode fingers reduce thedielectric constant between the fingers and necessitate, for a givenrate of heat-up, greater power inputs and a consequent loss inefiiciency of operation.

As best seen in FIG. 2 the spacing between each electrode finger 58,58', of both assemblies decreases from a maximum at the tow introductionend (the lefthand end as viewed in FIG. 2). Such electrode fingerspacing, labeled C in FIG. 3, is systematically decreased until itbecomes quite small at the tow departure end. Such an arrangement isfound to provide a dielectric field of increasing intensity as oneprogresses downstream in the direction of tow travel, a cardinal featurein dielectric drawing operations where polar moisturizing agents arebeing employed to accelerate heat-up rates. That is, the high moisturetow entering the upstream end of the electrode assembly possesses ahigher dielectric loss factor than the relatively drier tow passingthrough the downstream end of the assembly; therefore, a uniform heatingrate throughout the dielectrically heated drawing zone may be maintainedby increasing the field intensity as the moisture level of the towdecreases during heat-up, such an increasing field intensity being mostexpediently accomplished by means of the decreasing electrode fingerspacing just described.

A further advantage to be found in this electrode spacing arrangementlies in the fact that, in the regions of higher moisture, arcingpropensities are a maximum; that is, the threshold beyond whichelectrode arcing may occur is lower at the upstream end of the electrodeassembly than at the downstream end. Therefore, a higher field intensitymay be accommodated towards the downstream end where lower levels ofmoisture are encountered. This consideration joins very nicely with thatwhich grows out of the observation that the field intensity must beincreased in the face of decreasing moisture content if a substantiallyconstant heat-up rate is to be maintained.

The outer extremities of the electrode fingers 58, 58' of the upper andlower electrode assemblies are arranged to overlap an amount at leastequal to the width of the tow being processed, as seen in FIG. 2.However, this overlap should be maintained as small as possible in orderto provide maximum voltage density in the area served by each pair ofupper and lower fingers. As the mass and, consequently, width of towincreases, the overlap is necessarily increased to accommodate suchwidth and, if heat-up rate is to be maintained, the voltage mustaccordingly be increased to maintain a given field intensity. It willtherefore appear that, where it is contemplated that tows of variousdenier will be processed, either one or both of the upper and lowerelectrode assemblies should be mounted so as to be adjustable within theplane of FIG. 2 to thereby regulate the electrode finger overlap to thatminimum which will accommodate the width of tow being processed.Obviously, the length of the electrode assembly will be determined by,inter alia, the material being processed, draw speed and ratio, polarliquid content, and electrode spacing, both vertical and horizontal.

We have found the drawing of heavy denier tows during dielectricallyinduced heating to be of particular benefit in the case of polyethyleneterephthalate due to the fact that, within its optimum drawingtemperature range of 90 to 100 0, its dielectric loss factor approachesa maximum with the result that, as the tow is heated to drawingtemperature, the efiiciency of heat conversion increases for a giveninput of dielectric energy.

The principles and practice of this invention are further illustrated bythe following examples, which are not to be construed as limitative inthat any variations in materials and conditions elsewhere indicatedherein may be substituted in lieu of those set out in these examplesExample I The following example is illustrative of the practice of thisprocess in the absence of any preconditioning of the tow, i.e., the towwas drawn at ambient conditions of 65% relative humidity at atemperature of 22 C. A uniformly spaced electrode arrangement wasemployed under these relatively dry conditions.

Bobbins of as-spun continuous filament polyester yarn from severalspinning runs were placed upon a bobbin creel from whence the bobbinyarn ends were plied together into a unified tow bundle of 70,000 totaldenier. After plying, the tow was forwarded to a constant tension meansin order to facilitate placing the filaments of the tow bundle under asnearly uniform tension as was practicable.

From the tension means the tow bundle was forwarded by a pair of feedrolls operated at a peripheral surface speed of 11 f.p.m. The feed rollswere so arranged that one roll was canted with respect to the other topermit making sufficient wraps of the tow thereupon to prevent slippageduring drawing. In this instance 8 wraps were found sufiicient.

From the feed rolls the tow was forwarded to the dielectric oven,through the dielectric cell therein and out to a pair of draw rolls withone roll canted with respect to the other whereon 8 wraps of the tow wasmade. The draw rolls were operated at a peripheral speed of 54.5 f.p.m.The differential speed existing between the feed and draw rolls provideda draw ratio of 4.95:1. From the draw rolls the drawn tow was forwardedto a commercial take-up whereon the drawn tow is packaged onto a bobbinfor subsequent processing into staple yarn.

The dielectric cell utilized consisted of a pair of multifingeredelectrodes affixed to high and ground potential bus bars. The electrodesof the cell were arranged in a staggered, parallel and overlappingrelationship spaced apart a distance sufficient to permit the passage ofthe 70,000 denier tow bundle with a tangential contact being madebetween the tow and the electrodes. Each bus bar had affixed thereto 37finger electrodes spaced on /2 inch centers. Said electrodes were A inchin diameter.

Employing this cell, the tow bundle was subjected to a uniformly intensedielectric field strength of approximately 8500 volts per inch at anapplied voltage of 3000 volts at a frequency of 27 megacycles persecond. (The field intensity is calculated by dividing the voltage dropacross the electrodes by the distance existing between adjacent high andground potential electrodes. In the case at hand this distance was about0.35 inch.)

While in the confines of the cell the tow bundle was uniformly heatedthroughout its mass to a drawing temperature of C.

Subsequent to drawing the tow was cut into staple samples and examinedto determine their physical properties and the degree of level dyeing.These tests revealed the drawn staple had a filament denier of 1.91, atenacity of 6.55 g.p.d., an elongation of 32.1%, a modulus of g.p.d. andan average dark dye defect count per 100 grains of staple yarn of 45.

The dark dye defect count is determined, in the examples here set forth,according to a procedure wherein a drawn staple sample is prepared bycrimping approximately 100 grams of drawn tow to impart 10 to 12 crimpsper inch thereto. The crimped tow is then skeined and placed in a hotair oven and heated for 9 minutes at C. The heat set tow is then cutinto staple lengths of 1 to 1% inches and dyed (in the present examples,

Celliton fast blue AF dye was utilized). The dyed staple is then handcarded to remove tangles and open the staple bundle. Random samples arethen taken from the bundle, weighed to the nearest 0.001 gram and spreadto count the dark dyed fibers. This count per given weight of sample isthen converted to an average count for 100 grains, where 6.48 grams=100grains.

Example 11 The following example illustrates the process employing theuse of a polar moisturizing agent at ambient temperature using graduatedelectrode spacing.

A continuous filament polyester tow bundle of 63,000 total denier wasplied together as described in Example I. From the constant tensionmeans the tow was forwarded through a preconditioning chamber whereinwater at a temperature of C. was mist sprayed upon the tow. The towdeparted the preconditioning chamber after residing therein for 2.5seconds with a moisture level of 7.5% by weight of dry tow.

The moisturized tow was then forwarded by feed rolls of the sameconstruction as those in Example I operating at a peripheral speed of74.4 f.p.m. From the feed rolls, the tow was forwarded into a dielectricoven and through the dielectric cell housed therein wherein the tow waselevated to a uniform temperature of 90 C. by the dielectric energysupplied thereto to facilitate uniform drawing. While the tow was underthe influence of the dielectric field, it was simultaneously subjectedto drawing provided by a pair of draw rolls, as in Example I, operatedat a peripheral speed of 320 f.p.m. The differential in speed betweenthe feed and draw rolls provided a draw ratio of 4.3:1. From the drawrolls, the drawn tow was forwarded to a commercial take-up winder andwound on a bobbin for subsequent cutting into staple yarn.

The dielectric cell utilized was 42 inches in length with the fingerelectrodes arranged in a parallel and overlapping spaced relationship toprovide passage of the tow therethrough. The fingers were overlappedabout 1 inch to accommodate this size tow. The finger electrodes were /2inch in diameter and were spaced along the length of the cell at an everdecreasing center distance such that the widest electrode spacingoccurred at the tow entrance end to the cell and narrowest electrodespacing occurred at the tow exit end of the cell. As previously related,this electrode arrangement provides for an increasing field strength tobe applied to the tow as it progresses through the cell.

A voltage of 3000 volts at a frequency of 27 megacycles per second wasapplied to the cell electrodes. This voltage provided a field intensityvarying from approximately 1850 volts per inch at the tow entrance tothe cell to 3750 volts per inch at the tow exit end of the cell.

Subsequent to drawing the tow Was cut into staple lengths and evaluatedto reveal that the drawn denier was 1.52 d.p.f., with a tenacity of 5.31g.p.d., an elongation of 49.8%, a modulus of 45 g.p.d. and an averagedark dyed defect count per 100 grains of staple of 9. The moisturecontent of the drawn tow was less than 0.5%. The specific birefringenceof these samples was found to be 0.188 showing a high degree oforientation.

Example III The tow was forwarded from the tow bundle forming guide to aconstant tensioning means and thence into a preconditioning chamberwherein the tow was subjected to a water mist spray having a temperatureof 50 C.

I The tow departed the preconditioning chamber after residing thereinfor 1.7 seconds at a moisture level of 9% based on the weight of the drytow.

The preconditioned tow was subsequently forwarded by means of feedrolls, through the dielectric oven to draw rolls and thence to acommercial take-up winder for packaging onto a bobbin for laterprocessing into staple yarn. All of this equipment was identical to thatof Example II.

The feed rolls were operated at a peripheral speed of 76.4 f.p.m. andthe draw rolls at 320 f.p.m. to provide a draw ratio of 42:1. Thedielectric cell was operated at the same voltage and frequency as thatin Example II. The dielectric oven was operated at an environmentaltemperature of C. The moisture content of the drawn tow was measured tobe 0.3% by weight.

Subsequent to drawing, the tow was cut into staple yarn and tested forphysical properties and was found to have a denier per filament of 1.55,a tenacity of 5.7 g.p.d., an elongation of 44.0%, a modulus of 46 g.p.d.and an average dark dye count per grains of staple of 20. The specificbirefringence of these samples was measured to be 0.190.

Example 1V Bobbins of as-spun continuous filament nylon 66(polyhexamethylene adipamide) yarn from several spinning runs wereplaced upon a bobbin creel and plied together into a unified tow bundleof 40,000 total denier. After plying the tow, it was forwarded to aconstant tension means to impart as nearly a constant tension to eachfilament of the tow as was possible.

From the tension means, the tow bundle was forwarded by a pair of feedrolls operated at a peripheral speed of 31 f.p.m. The feed rolls werearranged as in Example I.

From the feed rolls the tow was forwarded to the dielectric oven,through the dielectric cell residing therein and out to a pair of drawrolls operating at f.p.m. The differential in speed existing between thefeed and draw rolls provided a draw ratio of 4.0: 1. From the draw rollsthe drawn tow was packaged onto a bobbin by a commercial take-up forsubsequent processing into staple yarn.

The dielectric cell, applied voltage, frequency and field intensityutilized were the same as described in Example I.

Physical examination of the drawn tow showed a tenacity of 5.12 g.p.d.,an elongation of 26.9%, a modulus of 35 g.p.d., a density of 1.145g./cc. and a birefringence of 0.523 (vs. 0.060 for normally drawn nylon66). This indicates the tow was not fully oriented.

Example V A bobbin of 840/ nylon 66 (tire yarn) was processedidentically as the tow of Example IV with the exception that a draw pinwas placed in the dielectric field to localize the draw point. One wrapof the yarn was made around the draw pin. The feed rolls were operatedat a peripheral speed of 19.61 f.p.m. and the draw rolls at 125 f.p.m.to provide a draw ratio of 6.37: 1.

Physical property examination revealed a tenacity of 9.33 g.p.d., anelongation of 10.9%, a modulus of 67.0 g.p.d., a density of 1.152g./cc., and a birefringence of 0.640.

It will now be appreciated that there has been herewith disclosed anovel and most beneficial process for the substantially dry-drawing ofheavy denier, high density tows of polyethylene terephthalate in anefficient and highly uniform manner, a process unattended by thedifficulties and expense typical of conventional wet-drawing operationsand which is productive of high quality tows exhibiting a high degree ofuniform orientation. Obviously, numerous modifications and variations ofthe present process are possible in the light of the above teachings. Itis, therefore, to be understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed herein.

What is claimed is:

1. The process of uniformly orienting polyethylene terephthalatefilaments in the form of a heavy denier tow simultaneously drawing saidtow under uniform tension ata pre-selected ratio to thereby draw-orientthe individual filaments comprising said tow at a uniform tem perature.

, 2. The process of claim 1 wherein the moisture content is within therange from about 6 to 12 percent.

3 3. The process of claim 1 wherein the dielectric field ischaracterized by a frequency of from 1 to 1200 megacycles and a voltagegradient of from about 2,000 to 25,000 volts.

4. The process of claim 1 wherein said dielectric field is characterizedby an increasing field intensity in the direction of tow traveltherethrough to thereby maintain 12 a substantially constant rateof,heat evolution insaid filaments.

5. The process of claim 1 wherein a continuous strearr of dry gas iscaused to sweep the space occupied by said dielectric field to therebyminimize electrode arcing tendencies. I

V References Cited UNITED STATES PATENTS 2,456,384 12/ 1948 Conaway28-62 2,692,875 10/1954 Weinstock et a1 260-855 3,032,856 5/1962Fleissner 28-595 3,081,485 3/1963 Steigerwald 219-1061 X 3,205,3349/1965 Manwaring 219-1061 3,263,052 7/1966 Jeppson et a1. 219-1061 X3,205,334 9/1965 Manwaring 219-1061 LOUIS K. RIMRODT, Primary Examiner.

